I had some trouble with this one, but I think that I got it figured out.
81R1E
I am curious about the thoughts of the experts here.
The Chase and Lund images aren't the greatest, so I included (3) copies that I have plates as 81R1E and one copy that I have plated as 81R1i for comparisons.
Disclaimer - There is no guarentee that these are plated correctly.
Example #2, with the 4 Bar Experimental NEW YORK cancel appears to have been plated by Chase. The other 2 examples have a position marking that I do not recognize the penmanship on.
The last image of this post, was plated by DSW (whose name escapes me at the moment - & I am blaming the recent covid bout for the memory loss and not old age) as 81R1i.
The patient that I was plating here appeared to have 2 guide dots in the lower right, but no such animal exists.
The new patient:

My three examples of 81R1E -
First Example:

Second Example - Appears to be plated by Dr. Chase:

Third Example:

And finally, the only example that I have of 81R1i, plated by DSW:

Sorry that I haven't been very active here. That covid bout ended in a little heart attack and I got behind at work. That's my excuse anyway.